The present invention relates in general to devices for producing trigger signals synchronized with the angular position of a rotating object and particularly to such a device wherein the number of trigger signals generated per revolution of the object is programmable.
In color copiers employing ink-jets it is necessary to coordinate the operation of an ink-jet with the angular position of a rotating drum. In an ink-jet copier, the copied image is formed on paper trained about the drum and as the drum rotates the ink-jets turn on and off spraying ink on the paper in a dot pattern to form the image. Changes in drum speed can cause errors in picture reproduction unless there is a compensating change in ink-jet triggering frequency. A similar problem can arise in coordinating the operation of a magnetic or laser recording head with the rotation of magnetic or laser activated disks or drums.
In the prior art it is common to attach a disk to the rotating object wherein the disk has been marked in some way at desired regular intervals about the disk. As the disk rotates the marks pass by a sensor (e.g. an optical sensor) which then produces a pulsed signal. The sensor signal may be used to trigger an external event to be synchronized with drum rotation, e.g. the imprinting of information.
In this method, the frequency of the triggering signal relative to the angular velocity of the drum is fixed by the number of marks about the disk. The disk must be changed if the external event is to be triggered more or less frequently with respect to drum rotation. It would be beneficial in many applications if the number of triggered events per revolution of the drum could be changed electronically without the need for changing the disk. For example in an ink-jet copier, this capability would facilitate adjustment of copier resolution.